Optical navigation and positioning system

ABSTRACT

An optical navigation system comprising a camera oriented to face towards a plurality of markers located at spaced apart locations from the camera, calculating means adapted to calculate an angle subtended between pairs of markers, the subtended angles being calculated by monitoring the pixel locations of the markers in a series of images captured by the camera, the optical navigation system additionally comprising means for creating a three-dimensional model whereby the location of the camera relative to the markers is determined by triangulating the subtended angles in the three-dimensional model.

This patent application is a U.S. National Stage patent application ofInternational Patent Application No. PCT/GB2014/050624, filed on Mar. 3,2014, which claims priority to United Kingdom Patent Application No.1303712.2, filed on Mar. 1, 2013.

This invention relates to an optical navigation and positioning system,suitable for use with cameras, and in particular, but withoutlimitation, to optical navigation systems for cameras used in film andtelevision filming environments, such as studios, on location or inoutdoor studios.

Video cameras are often used in studios, and nowadays, are oftenintegrated with Computer Generated Imagery (CGI) systems by whichcomputer-generated images can be composited with the actual footage shotto create an augmented image in the outputted video. The use of CGI isextremely widespread, and is replacing the use of physical “sets” andbackdrops in many film and television productions. CGI offers a numberof advantages over traditional sets, in terms of realism, versatilityand cost. Where the camera is static, it is relatively simple tocomposite the shot footage with CGI imagery to create the final renderedshot.

However, where the cameras need to move around the set, such as whenpanning and tracking, for example, the CGI compositing software needs toknow the precise location of the camera relative to fixed points inorder to create realistic CGI footage. If the camera's location is notprecisely known, then the CGI software will fail to realistically renderperspective, scale and shadows, for example, which can degrade the imagequality of the composited video footage.

Existing CGI systems therefore integrate with the camera supports, whichcomprise tracking devices so that the instantaneous locations of thecameras can be fed into the CGI software to facilitate the renderingaccurate CGI footage. Existing camera tracking systems comprise digitalencoders, which monitor the yaw, pitch and roll of the camera, its focallength, zoom setting and so on. Existing camera tracking systems mayadditionally comprise ball trackers, which have a ball that rolls overthe floor: the rotation of which is monitored using encoders todetermine the camera's location by dead reckoning. By fitting aplurality of ball trackers to a camera's support, it is possible tocalculate the support's position and rotation relative to, say, a studiofloor.

Ball tracker systems, however, need to be regularly re-calibrated asthey have a tendency to “drift”, that is to say, provide unreliable datashould one of the balls skid on the floor surface. Over time, therefore,each camera needs to be returned to a known position at intervals, and“reset” so that accumulated errors and drift in their ball tracker'smeasurements can be “zeroed out”. The fact that the camera's positionmeasurement is susceptible to errors and drift renders ball trackersystems unreliable, or at least insufficiently robust, in many filmingsituations.

A known alternative to mechanical measurement techniques, such as balltrackers, is to use optical navigation systems whereby a dedicatedcamera scans the studio ceiling for pre-placed markers or targets. Thepixel locations of the markers in the ceiling-facing camera's images canbe mapped onto a 3D computer model of the studio or the 3D model of themarkers to enable the camera's location to be precisely triangulated.Optical navigation systems of this type are generally more reliable thanball tracker systems because as they are not susceptible to drift, themarkers' locations being fixed in space. However, existing opticalnavigation systems rely on the accurate placement of the markers, andthe accurate insertion of each marker's position in the 3D model: witheven small inaccuracies potentially leading to large errors in thecalculated position of the camera. As such, existing optical navigationsystems for cameras need markers to be installed on an accurate gridsystem, which needs to be carried out using specialist surveyingequipment, such as theodolites. In most cases, existing opticalnavigation systems work relatively well, but in a studio environment,where ceiling lighting etc. is adjusted regularly, and where there is ahigh probability of collisions between the ceiling markers and cranes ortechnicians rearranging lights or other ceiling hung equipment, say,they can be susceptible to failure.

A need therefore exists for an optical navigation system that does notrely on an absolute reference frame system, but rather one that can use“natural markers”, such as existing features of a room's ceiling, andwhich can adapt to changes in the reference system.

Non-absolute optical navigation systems are also known, which make useof so-called “SLAM” (Simultaneous Localisation and Mapping), whereby athree dimensional model of a room based, say, on a number of images ofthe room's ceiling, can self-calibrate and update as the camera movesaround. In general terms, SLAM works by measuring how the angle ofseveral points of interest in an image shift relative to one another asthe viewpoint moves. The angles are calculated by comparing pixellocations of the points of interest in the image from the centre pixelpositions, which is assumed to like approximately on the optical axis ofthe view point, to obtain vectors to the points of interest. Rather thanrelying on an image based (bitmap) analysis process, as is the case inabsolute optical navigation systems, SLAM systems build a threedimensional model based on vector angles, which is considerably moreaccurate, and which can determine not only the track (X & Y coordinates)location of the camera on the floor, but also its rotation relative tothe room, and its elevation (Y-coordinate). SLAM systems can be veryaccurate.

A problem that is particular to SLAM systems used in studio filmingenvironments is that of “blinding” the ceiling-facing optical navigationcamera by the set lighting. Film set lighting tends to be very bright,which can obliterate the visible features that ceiling-facing SLAMsystems need to work effectively.

A need therefore exists for an improved and/or alternative opticalnavigation system that addresses or overcomes one or more of theproblems outlined above.

According to a first aspect of the invention, there is provided anoptical navigation system comprising a camera oriented to face towards aplurality of markers located at spaced apart locations from the camera,calculating means adapted to monitor, in a series of images captured bythe camera, the pixel locations of the markers, the optical navigationsystem additionally comprising means for creating a three-dimensionalmodel of the camera's position and orientation relative to the markersby monitoring changes in the relative positions of the markers in thecaptured images to determine, by monitoring changes in the apparentperspective of the markers that are indicative of changes in orientationand position of the markers.

Suitably, the markers are randomly located or positioned, i.e. notaccurately measured out.

The invention therefore provides an optical navigation system that fallssomewhere between an accurate triangulation system in which the markersare placed a precise and known locations, and a SLAM system which usesnatural features, such as the corners of a room or ceiling features, todetermine the position and/or location of the camera. The invention, bycontrast, provides a solution falling somewhere between these extremes,that enables randomly-placed markers to be used to improve theeffectiveness of SLAM, whilst avoiding the need for the accurateplacement of the markers, as is the case in a triangulation system. Incertain embodiments, therefore, the invention overcomes one or more ofthe drawbacks of know systems, as outlined above.

According to a second aspect of the invention, there is provided anoptical navigation system comprising a camera oriented to face towards aplurality of markers located at spaced apart locations from the camera,calculating means adapted to calculate an angle subtended between pairsof markers, the subtended angles being calculated by monitoring thepixel locations of the markers in a series of images captured by thecamera, the optical navigation system additionally comprising means forcreating a three-dimensional model whereby the location of the camerarelative to the markers is determined by triangulating the subtendedangles in the three-dimensional model.

A third aspect of the invention provides an optical navigation systemcomprising a camera oriented to face towards a plurality of markerslocated at spaced apart locations from the camera, calculating meansadapted to calculate an angle subtended between pairs of markers, thesubtended angles being calculated by monitoring the pixel locations ofthe markers in a series of images captured by the camera, the opticalnavigation system additionally comprising means for creating athree-dimensional model whereby the location of the camera relative tothe markers is determined by triangulating the subtended angles in thethree-dimensional model, and wherein the optical navigation systemfurther comprises a light source located proximal to the camera andbeing arranged to project light away from the camera in the direction ofthe markers, and wherein the markers are retroreflective.

A fourth aspect of the invention provides an optical navigation systemcomprising two or more spaced apart cameras oriented to face towards aplurality of markers located at spaced apart locations from the cameras,calculating means adapted to calculate an angle subtended between pairsof markers, the subtended angles being calculated by monitoring thepixel locations of the markers in a series of images captured by thecameras, the optical navigation system additionally comprising means forcreating a three-dimensional model whereby the location of each camerarelative to the markers is determined by triangulating the subtendedangles in the three-dimensional model. Suitable, one of the cameras isarranged to point at placed markers or using natural markers.

A fifth aspect of the invention provides an optical navigation systemcomprising a camera oriented to face towards a plurality of markerslocated at spaced apart locations from the camera, calculating meansadapted to calculate an angle subtended between pairs of markers, thesubtended angles being calculated by monitoring the pixel locations ofthe markers in a series of images captured by the camera, the opticalnavigation system additionally comprising means for creating athree-dimensional model whereby the location of the camera relative tothe markers is determined by triangulating the subtended angles in thethree-dimensional model, and wherein the optical navigation systemadditionally comprises an attitude sensor.

Suitably, the attitude sensor comprises either or both of an opticalattitude sensor and a gyroscope.

By providing a light source next to the camera and by making the markersretroreflective, it has surprisingly been found that the markers “standout” in images captured by the camera, even where the markers arelocated near to light sources facing towards the camera of the opticalnavigation system. Such an arrangement has been found to overcome theproblem of the camera being blinded by bright ceiling lighting, which iscommonly found in film and TV studios.

The known solution to the problem of “blinding” of the opticalnavigation system's camera by ceiling lighting has been to position someor all of the markers on the floor or walls of the studio, but by sodoing, the markers can appear in the shot footage, which is highlyundesirable. By using retroreflective markers, the markers can be placedon the ceiling, even where ceiling lighting is used.

Notably, the markers can be positioned at random locations or evenmoved, and the calculating means is able to “learn” its position by theapparent movement of the markers as the camera is moved in threedimensional space. Thus, even where certain markers are removed oradded, the system is able to notice this and to compensate accordingly.The invention thereby overcomes the problem of the need for precise,fixed installation of the markers.

Where the optical navigation system comprises two or more cameras, themeasurement of the camera's position is performed in stereo, therebyproviding some redundancy. A further advantage of using two or morecameras, especially where they are arranged to face in differentdirections, is that the accuracy of the navigation system can be greatlyimproved because both cameras can be used to determine the locationand/or attitude of the system using difference markers simultaneously.

One of the additional cameras may be arranged to point towards an objectbeing filmed by a movie camera, in which case, a stereoscopic image ofthe subject, e.g. an actor, can be obtained to enable thethree-dimensional form of the subject to be ascertained. By measuringthe form of the subject at the time of capturing the video footage, itis possible to integrate this additional information into a connectedCGI system to obtain improved rendering of shadows and lighting effects,etc. in the composited footage.

Where an optical attitude sensor is used, the optical attitude sensorsuitably comprises a lighting system adapted to project a grid-likepattern of, say, infra-red light, towards a floor surface. By using“invisible” light, the projected light pattern does not affect, or showup in, movie footage shot simultaneously therewith.

The optical attitude sensor suitably comprises a light detector, such asan IR camera, which interprets the IR grid, as seen by the lightdetector, to ascertain the distance from a surface and the attitude ofthe system relative to the surface. By providing, say, a floor-facingoptical attitude sensor in conjunction with an optical navigation systemas described herein, the robustness of the measurement of the camera'sposition, elevation and attitude can be improved. The optical attitudesensor suitably comprises a Microsoft® Kinect™ system.

Additionally or alternatively, the attitude sensor may comprise agyroscope rigidly affixed to the camera. A gyroscope, in certaincircumstances, can provide a very accurate, and almost instantaneous,measurement of the camera's attitude. However, gyroscopes aresusceptible to “drift” over a period of time. On the other hand, anoptical navigation system, such as that described herein, is moreaccurate, over time, but due to the computation involved, can be slowerto react. Therefore, by combining a gyroscope with an optical system asdescribed herein, the invention can provide the best of both worlds,that is to say, the option to cross-compare the outputs to providecorrection of one system or the other in real time.

Preferred embodiments of the invention shall now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic perspective view of an optical navigation systemin accordance with the invention;

FIG. 2 is a series of schematic images of the markers as viewed by thecameras of the optical navigation system of FIG. 1; and

FIG. 3 is a schematic construct of the images of FIG. 2.

In FIG. 1, an optical navigation system 10 according to the inventioncomprises a movie camera 12 mounted for movement on a wheeled tripod 14so that the movie camera can track X, Y, elevate Z, pan P, roll R andtilt T in accordance with an operator's (not shown) inputs. The moviecamera 12 is fitted with an optical navigation system 10 comprising aceiling facing camera 16 and a forward facing camera 18, the latterbeing fixedly aligned, but offset, with respect to the optical axis 20of the movie camera 12 so that its optical axis 22 is parallel to thatof the movie camera's 20. The movie camera 12 can thus capture videofootage of a subject 24.

The studio in which the optical navigation system is installedadditionally comprises a random or regular array of markers 26 stuck tothe ceiling (not shown), lighting rails (not shown) or other objectslocated above the camera 12. Some of the markers 26 are retroreflectiveand the ceiling-facing camera 16 is fitted with an annular ring of LEDs28 around its lens, which LEDs project a beam of visible light towards,and for illuminating, the markers 26.

The LEDs are mounted on a self-levelling mount, which may be activelydriven by sensors or encoders, or it may be adapted to self-level underthe effect of gravity (e.g. a gimbal). The levelling mechanism, whereprovided, makes sure that LEDs are pointing up towards the ceiling evenwhen the main camera 12 is tilting up or down, or rolled. An advantageof this configuration is that the LEDs do not dazzle or blind the actorsor interfere with set lighting.

In an alternative embodiment of the invention, several LEDs are disposedon a curved or arcuate surface, such as a dome. The system is suitablyprovided with an attitude sensor and the LEDs are individuallyswitchable, or switchable in groups, so that only the LEDs that arefacing upwardly are illuminated at a given point in time. Such aconfiguration ensures that at least some upwardly facing LEDs areilluminated, to illuminate markers placed above the system, whilstavoiding LEDs from shining towards the scene being shot, i.e. towardsactors, which may be dazzling, distracting or otherwise undesirable,e.g. interfering with set lighting, as the camera is panned, tilted, orrolled.

The ceiling-facing camera 16 captures video footage of the area abovethe camera 12, which footage includes footage of the markers 26. Bymoving the camera X, Y, X, P, R, T, the positions of the markers 26 inthe field of view of the ceiling-facing camera 16 change, as shall beexplained below.

Also shown in FIG. 1 of the drawings is a floor-facing, optical attitudesensor 30, which projects a grid 32 of infrared light towards the floor.The optical attitude sensor 30 additionally comprises an infrared cameraand a processor adapted to interpret the grid pattern that it “sees” todetermine the pitch P, roll R and tilt T angle of the camera 12. Inaddition, if correctly calibrated, the optical attitude sensor caninterpret the infrared grid 32 to determine the elevation Y of thecamera 12 above the floor.

The optical attitude sensor 30 is essentially a depth sensor, givingpoints with distance at various positions in its field of view. Bypointing the optical attitude sensor 30 towards the floor, it ispossible to obtain a normal vector to the floor by assuming that thelargest plane is the floor. The largest plane is a plane that passesthrough a furthest point in the picture or a plane that passes throughthe largest number of coplanar points. Measuring the normal vector willprovide pan, roll and height information. By using a plane representingthe floor, it is possible to reliably disregard points corresponding toobstructions in the field of view of the optical attitude sensor 30,such as the legs of the tripod, as shown in FIG. 1.

FIG. 2 is a series of images as captured by the ceiling-facing camera16, in which the markers 26 and other “natural” features 34 of theceiling are visible. The captured video footage is essentially a bitmapimage in which the markers 26 are placed at particular pixel locations.If the camera has a known field of view angle, the angular separation ofpoints of interest in the captured images, in this case, the centres ofthe markers 26, will be a function of the number of pixels between thosecentres. Crucially, the distance to each point of interest is not known,nor is it needed, because the image lies in a virtual plane with theapparent positions of the markers 26 lying at known angular separations,thus yielding a pointing vector from the ceiling-facing camera 16 toeach point of interest.

The optical navigation system “tracks” the movement of the markers 26,36 in the images, and can compare their apparent positions fromframe-to-frame of captured footage, enabling their relative positions tobe calculated by triangulating the vectors. Thus, if the camera movesdirectly towards a particular marker, the apparent position of thatmarker will remain substantially constant. However, there will be a“zooming” effect visible in respect of the other markers, enabling thepositions of the other markers to be calculated in three-dimensionalspace. Likewise, rotation of the ceiling-facing camera 16, for example,as the camera pans, will be detected as rotation of the markers 26 inthe captured footage about various loci depending on their relativepositions in actual space. Thus, the ceiling-facing camera 16 of theoptical navigation system is capable of detecting movement of the moviecamera 12 in three-dimensional space, in all six axes X, Y, X, P, R, andT.

In FIG. 3, it can be seen how the apparent positions 26′ of the markers26 changes as the camera 16 moves from a first position to a secondposition 16′. The camera 16 identifies, in the illustrated example, twomarkers 26, which are at different distances from the camera 16.However, the camera 16 is only able to recognise line of sight, and notdistance, so the apparent positions 26′ of the markers 26 is shown in avirtual plane corresponding to the image plane. In the virtual plane,the distance d1 between the apparent positions of the markers 26′ isrelated to the separation angle θ in three-dimensional space between theactual markers 26, as measured from the viewpoint of the camera 16.

In the second frame of FIG. 2, the camera 16 has moved to a differentposition and this is shown in FIG. 3 as 16′. The actual positions of themarkers 26 in three-dimensional space remain the same, but theirapparent positions 26″ in the virtual image plane are shifted due to thechange of viewpoint. Thus, the angle subtended ϕ, between the markers 26is evident from a change of separation d2 in the image captured by thecamera 16. By repeating this process from frame to frame, and byassuming that the positions of the markers 26 remains substantiallyconstant, it is possible to triangulate the position of the camera 12relative to the markers 26.

The use of retroreflective markers 26 alleviates or overcomes theproblem of the markers becoming invisible when they are positioned closeto floor-facing lights, i.e. towards the ceiling-facing camera 16. Italso allows the markers to be used in lower level lighting conditions.

One or more of the placed markers 26 may comprise characteristicfeatures, e.g. being of a particular shape or comprising a barcode, sothat they can be automatically identified by a machine vision system.These markers may be precisely positioned to help scale all of theremaining markers, or to facilitate recalibration after having moved orremoved one or more of the other markers. Surprisingly, it has beenfound that by placing a characteristic marker in each corner of theroom/studio/set, it is possible to recalibrate the system more quickly.

The forward facing camera 18 captures a secondary image of the subject24, providing valuable depth information, which can be used by aconnected CGI compositing system (not shown) for more accuratelyrendering CGI shadows and lighting effects. Moreover, the forward-facingcamera can also implement a secondary optical navigation routine,similar to that described above in relation to the ceiling-facing camera16, albeit relying solely on “natural” features in its captured footagebecause it is undesirable to “clutter” the subject of the movie footagewith markers 26, although they may be provided as well.

The forward facing camera 18 is used to monitor natural or placedmarkers in the field of view of the main camera 12, which can be used toprovide viable information about the lens characteristics of main camera12. The forward-facing camera 18 is suitably calibrated precisely,whereas the main camera 12 is often not calibrated as precisely becausethere is no time to do so on set and because zoom lenses changecharacteristics when zooming and focusing. Whilst encoders may beassociated with the main camera 12 for determine the zoom and focussettings, the encoders generally lack the degree of accuracy needed byCGI systems. By using the forward-facing camera 18 in conjunction withthe main camera 12, it is possible to calculate the instantaneous lensdistortion of the main camera 12, which helps to add in the apparentdistortion of the main camera 12 into the composited CGI image or model:i.e. the CGI distortion can be made to match that of the main camera 12for a more realistic result.

In addition, by using a forward-facing camera 18, one can use natural orplaced markers or reflective 3D information to be used in matching thevirtual (CGI) world to features in the real world. For example, it ispossible to snap a virtual floor to areal floor, to snap virtual wall toreal wall or to snap a virtual table top to real one.

The optical navigation system of the invention may be used to supplementor replace a conventional ball tracker navigation system. The data fromthe optical navigation system is suitably fed into a CGI compositor asthe camera position and attitude data that the CGI system requires to beable to composite realistic CGI footage.

Applications for the invention exist in technical fields other thanstudio filming, for example, in medical imaging applications.Specifically, the position of the tip of an endoscope could bedeterminable using a system in accordance with the invention, by, sayattaching a camera to the grip or shaft of the endoscope which pointstowards a patient's body. Markers could be affixed to the patient's bodyin the area surrounding the insertion point of the endoscope such thatthe position of the tip of the endoscope, which may be fixed relative tothe camera, could be ascertained by monitoring, in the camera's images,the relative positions of the markers from frame to frame. The positiondata of the tip of the endoscope could be transposed into, say, a 3D MRIimage of the patient's body so that the surgeon can see a virtualrepresentation of the tip of the endoscope in the MRI image, in realtime. Such a system could reduce, or obviate the need to actually imagethe patient with the endoscope in-situ.

The invention is not restricted to the details of the foregoingembodiments, which are merely exemplary of the invention. For example,the optical navigation system may or may not include a forward facingcamera, the “forward facing” camera may be angled away from the opticalaxis of the main movie camera or the ceiling-facing camera, the opticalattitude sensor may be omitted, the movie camera may be mounted on adifferent type of mounting system, such as a ceiling track etc., allwithout departing from the scope of the invention.

The invention claimed is:
 1. An optical navigation system comprising; acamera; a plurality of randomly positioned retroreflective markerslocated at spaced apart locations from the camera, wherein it is assumedthat the positions of the markers remain substantially the same; thecamera being configured to capture a series of images in which at leastsome of the markers are visible, the series of images being essentiallybitmap images in which the markers are placed at particular pixellocations; and a processor configured to: monitor, in the series ofimages captured by the camera, the pixel locations of the markers,determine a distance between pairs of markers in the captured images,said distance being related to a separation angle in three-dimensionalspace between the actual markers, as measured from the viewpoint of thecamera, and monitor changes of distance between pairs of markers in theimages captured by the camera, repeating this process from frame toframe, and triangulating the position of the camera relative to themarkers.
 2. The optical navigation system of claim 1, the processorbeing further configured to determine the camera's position relative tothe markers by determining the angular separation between pairs ofmarkers in the captured images, the angular separation being a functionof the number of pixels in the captured images between each pair ofmarkers.
 3. The optical navigation system of claim 1, further comprisinga light source located proximal to the camera and being arranged toproject light away from the camera in the direction of the markers, thelight source comprising an annular ring of LEDs surrounding the cameralens, the LEDs being arranged to project a beam of visible lighttowards, and for illuminating, the markers, and the light source beingoptionally mounted on a self-leveling mount being any one or more of thegroup comprising: a gimbal; and an actively driven mount comprising anattitude sensor and a transducer for maintaining the light source in adesired orientation relative to the horizontal.
 4. The opticalnavigation system of claim 1, further comprising a light source locatedproximal to the camera and being arranged to project light away from thecamera in the direction of the markers, the light source comprising aplurality of LEDs disposed on a curved or arcuate surface, and the lightsource comprising an attitude sensor and wherein the LEDs areindividually switchable, or switchable in groups, so that only the LEDsthat are facing substantially upwardly are illuminated at a given pointin time.
 5. The optical navigation system of claim 1, at least one ofthe markers comprising a characteristic feature comprising any one ormore of the group consisting of: the marker being of a particular shape;the marker comprising a barcode; and the marker being automaticallyidentifiable by a machine vision system.
 6. The optical navigationsystem of claim 1, comprising two or more spaced apart cameras orientedto face towards a plurality of markers located at spaced apart locationsfrom the cameras, the cameras being arranged to face in differentdirections, at least one of the cameras comprising a forward-facingcamera being arranged to point towards an object being filmed by a moviecamera configured to capture a secondary image of the subject of themovie camera.
 7. The optical navigation system of claim 6, the secondaryimage being used to implement a secondary optical navigation routinerelying solely on natural features in its captured footage.
 8. Theoptical navigation system of claim 1, further comprising any one or moreof the group comprising: an optical attitude sensor comprising alighting system adapted to project a grid-like pattern of light, towardsa surface and a light detector adapted, in use, to interpret thegrid-like pattern in its field of view to ascertain a distance from thesurface and an attitude of the system relative to the surface, theoptical attitude sensor comprising a depth sensor adapted to determinepoints with distance at various positions in its field of view; anattitude sensor comprising a gyroscope; and a ball tracker navigationsystem.
 9. A system for capturing video footage comprising a moviecamera moveably mounted on a moveable support for movement in 6 axes(track-X, track-Y, elevate, pan, roll and tilt), an optical navigationsystem according to claim 1 rigidly affixed, for movement in unisonwith, the movie camera, and a plurality of retroreflective markerslocated at fixed positions above the movie camera.
 10. The system ofclaim 9, the optical navigation system comprising a ceiling-facingcamera and a forward-facing camera, the forward-facing camera beingfixedly aligned, but offset, with respect to an optical axis of themovie camera such that the forward-facing camera's optical axis issubstantially parallel with, but offset relative to, the optical axis ofthe movie camera.
 11. The system of claim 9, further comprising a CGIcompositor and the optical navigation system being configured to providecamera position data for the CGI compositor.
 12. The system of claim 9deployed in a film studio, the markers being disposed in a random orregular array of markers on a ceiling, lighting rails or other objectslocated above the movie camera.
 13. An endoscope comprising an opticalnavigation system according to claim 1, the camera being rigidly mountedto the shaft of the endoscope and the markers comprising self-adhesivemarkers affixable, in use, to a patient's body at positions surroundingor proximal to the insertion point of the endoscope.
 14. The opticalnavigation system of claim 1, further configured to track the movementof the camera by comparing the apparent positions of the markers in theimages from frame-to-frame of captured footage.
 15. The opticalnavigation system of claim 14, tracking the movement of the cameracomprising detecting a zooming effect in the apparent positions of themarkers.
 16. The optical navigation system of claim 14, tracking themovement of the camera comprising detecting rotation of the camera bydetecting rotation of the markers in the captured images about variousloci depending on their relative positions in actual space.